1. Field of the Invention
The invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device which has its display screen formed of a plurality of laminated liquid crystal layers.
Also, the invention relates to an inter-connector for interconnecting a plurality of opposed conductive layers with interposing an insulating layer.
The invention relates to a liquid crystal display device having a liquid crystal layer with high reflectance or absorption of light.
2. Description of the Related Art
The liquid crystal display device, which is thin and consumes merely a low power, is now used for the display screens of OA equipment such as PCs (personal computers), word processors and EWS; displays of electronic calculators, Electronic Book (trademark), electronic organizers and PDAs; and TV monitors and in many other fields. The liquid crystal display device is particularly characterized by its low power consumption as compared with other displays such as CRTs and plasma displays. And its application is expected to be expanded further to notebook PCs, PDAs, portable TVs, portable telephones, portable FAXs and other portable information-processing equipment. Such portable information-processing equipment must be battery-driven, and its display device must use lower power. The display device for the portable equipment is desired to have low power consumption of 500 mW or below, more preferably several mW.
Among other liquid crystal display devices, one having a display screen on which images are directly seen is called a direct-vision type. The direct-vision type liquid crystal display device includes a transmission type which has a light source such as a fluorescent lamp on the back of a liquid crystal cell and a reflection type which uses surrounding light to display. The former needs the backlight and, therefore, it is not suitable to be a low power consumption type. The backlight has power consumption of 1 W or more, and if batteries are used, its usable time is limited to about two to about three hours. Therefore, the reflection type liquid crystal display device is often used for the display screen of the portable electronic equipment such as portable information-processing equipment.
Conventionally, a TN-type liquid crystal was used for a reflection type simple matrix liquid crystal display device. But, the liquid crystal display device having the TN-type liquid crystal needs a polarizing plate, and its reflectance is limited to about 30%. Therefore, there is a disadvantage that the display screen is dark. Additionally, the simple matrix liquid crystal display device has a disadvantage that a contrast lowers when the number of pixels is increased and the display quality is also lowered.
Accordingly, for the reflection type liquid crystal display device, a GH (guest host) display mode not requiring a polarizing plate is most promising in view of the light utilization efficiency. It is now being tried to employ the GH mode to make the active matrix drive in order to achieve a liquid crystal display device having a high reflectance and a high contrast.
To achieve a color display on the reflection type liquid crystal display device, there is an ECB mode (electrically controlled birefringence) to control a reflected wavelength by an applied voltage, but it has a disadvantage that a displayable color range is narrow. In addition, there is also a known method that a picture element is configured by disposing RGB pixels configured by using, for example, a color filter on a plane surface.
Generally, it is most preferable to configure using the GH liquid crystal cells laminated to achieve the color display having a wide color reproduction range by the reflection type liquid crystal display device. On the other hand, an array arrangement of the RGB pixels in a same plane or an array arrangement of C(cyan), M(magenta) and Y(yellow) pixels in a same plane cannot display the same color by all pixels. Therefore, a reflectance is low, display is dark, and a color reproduction range is narrowly restricted.
FIG. 17 is a schematic diagram showing the structure of a conventional liquid crystal display device having parallel-arranged RGB pixels.
In the figure, 980 is an array substrate, and a switching TFT 987 for supplying a potential to a reflection pixel electrode 982 is formed thereon. In addition, 985 is a counter substrate, and a counter electrode 984 is formed to cover a color filter 986 formed on the surface of the counter substrate 985. Additionally, a guest host liquid crystal 983 is interposed between the array substrate 980 and the counter substrate 985. By configuring as described above, full-color display can be made in principle. But, since pixels of the three primary colors are arranged in parallel to configure the picture element, each of the three primary colors is limited to reflect on an area about 1/3 of the picture element. Thus, there are disadvantages that a light using efficiency is poor, and the screen becomes dark.
For example, a known liquid crystal display device for color display by the GH method has three-layered GH mode liquid crystal cells respectively containing pigments of the three primary colors cyan, magenta and yellow. With this liquid crystal display device having the three layered structure of the subtractive primary colors cyan, magenta and yellow, the light using efficiency can be improved.
But, the liquid crystal display device of a type configuring the picture element by laminating a plurality of pixels as described above is hard to apply a display signal voltage to each of the plurality of laminated liquid crystal layers, and the cost becomes high. Especially, when the display signal is applied from the substrate side to the pixel electrode interposed between the laminated liquid crystal layers, the liquid crystal display device has a complex structure, its productivity is lowered, and the cost becomes high.
To configure the liquid crystal display device having the GH mode, there is another subject to be achieved that the light reflection efficiency or absorbing efficiency of the GH liquid crystal layer is improved. If the incident light can not be reflected or absorbed fully by the liquid crystal layer, the quality of display is degraded.